The following description is provided to assist the understanding of the reader. None of the information provided or references cited is admitted to be prior art.
The modification of carbohydrate can be divided into two main types: chemical and rheological. Chemical modification generally refers to the substitution of a carbohydrate with chemical groups, which changes the charge condition of the carbohydrate or increases the stability. Chemical modification of carbohydrates generally occurs via the introduction of functional groups that change the carbohydrate properties. The properties of modified carbohydrates depend on the type of functional group or substituents as well as the degree of substitution. Modification can be achieved by various methods such as bleaching, oxidation, acetylation, acid modification, etherification, esterification, cross-linking, etc. Rheological modifications are generally used when higher dry matter contents are desirable in a solution, which means decreasing the viscosity by hydrolysis or oxidation. For hydrolysis, enzymes or acids can be used. Acid conversion is performed by adding acid to hydrolyze the starch and reduce viscosity.
Oxidation is one of many types of carbohydrate modification processes. Oxidation is the transfer of electrons between an oxidant and a reducing end, which leads to degradation of polymer chain lengths and formation of carbonyl and carboxyl groups on the carbohydrate molecule. Oxidation generally involves treating the carbohydrate with bromine, chlorine or the corresponding metal hypohalite in an alkaline aqueous medium, e.g., the treatment of carbohydrate with hypochlorite, such as sodium hypochlorite. Hypochlorite oxidation of carbohydrates, although commonly employed in the industry, is known to be associated with drawbacks such as generation of chlorinated volatile organic compounds (VOCs), some of which are toxic and probable human carcinogens, have relatively short shelf-life and bio-treatment inhibition due to overdosing.
Regarding starch, for example, oxidation typically involves opening and cleavage of various linkages in the starch molecule. Starch is a glucose polymer which consists of glucose units linked together by ether bonds at the 1,4 points on the glucose ring to make the linear backbone, with additional branches to the polymer linked at the 1,6 unit on the ring. Oxidation will cleave these ether linkages, reducing molecular weight of the starch molecules. In addition, they can also cleave the glucose ring between the 2, 3 units, and can additionally convert one or both of these resulting aldehyde groups to carboxyls. The choice of oxidant, amount of alkali, temperature and reaction time can cause different rates of thinning as well as vary the amount of carboxyls produced in the thinned starch through the oxidation process. Other selective oxidants, like periodate, will only attack certain bonds on starch, with periodates attacking the
2-3 linkage. Some of the predominant reactions taking place during starch oxidation are: (a) oxidation of primary hydroxyls at C-6 position to carboxyl groups forming uronic acid; (b) oxidation of secondary alcohols to ketones; (c) oxidation of glycols at C-2 and C-3 position to aldehydes; and (d) oxidation of aldehyde end groups to carbonyl groups. Oxidation of starch may, therefore, result in the formation of a mixture of carbonyl and carboxyl groups.
Free radical chemistry has not been used extensively in commercial carbohydrate or starch manufacture. Free radicals are created when an unpaired electron is induced on a material, either through a chemical initiator or cleavage of a chemical bond. The radical electron is very unstable and will react readily with many materials. One example of a free radical is a hydroxyl radical, which is formed when a peroxide material such as hydrogen peroxide is cleaved into radicals. This can be accomplished by treating the material with excited energy such as ultraviolet light. Free radical reactions typically proceed continuously as long as there is a feed source for reaction. Feed sources and types of free radical reaction can vary significantly. In free radical polymerization, the feed source is monomer and the reaction creates a polymer from free radical linkages. As long as the monomer is present, the reaction proceeds. In free radical sterilization, the feed source is ultraviolet light and the reaction is a disruption or cleavage of chemical bonds. Likewise, in this case, the reaction proceeds as long as UV energy is supplied. However, free radical reactions will typically have a residual radical or radical source material after the reaction. This lets the free radical reaction continue to proceed as long as the chemical or energy acting as a feed source is present. Many chemicals that can function in one chemistry, such as oxidants, can also be used in free radical reactions if they are treated with a sufficient level of reactive energy, such as ultraviolet light.
In the present specification, all parts and percentages are on a weight by weight basis unless otherwise specified.